This invention relates to specific binding members for human carcinoembryonic antigen (CEA) and materials and methods relating thereto.
CEA is a tumour-associated glycoprotein, the expression of which is increased in a number of human carcinomas. CEA is a widely used clinical tumour marker, and antibodies raised against it have been used for imaging (Goldenberg, D. M. Int. J. of Biol. Markers 1992, 7; 183-188) and therapy (e.g. Ledermann et al., Int. J. Cancer 1991, 47; 659-664). CEA is a member of the immunoglobulin superfamily and has homology with a number of other antigens, such as normal cross-reacting antigen (NCA), found on normal tissues (Buchegger, F. et al., 1984, Int. J. Cancer 33; 643-649.).
A number of mouse anti-CEA antibodies exist binding to a range of epitopes on CEA (Hammarstrom et al., 1989, Cancer Res. 49, 4852-4858) and human anti-CEA antibodies have been isolated from human phage display libraries (A.D. Griffiths et al. EMBO J. 12, 1993; 725-734; A. D. Griffiths et al. EMBO J. 13 3245-3260, 1994; WO93/11236) The present invention results from the inventors having obtained the first example of human anti-CEA antibodies with a dissociation constant of less than 10 nM for CEA (1.times.10.sup.-8 M) and the first which do not cross-react with cell types which express NCA or with a normal human liver cell line.
Herein it is shown that large universal phage display libraries may be used as a source of human antibodies specific for human CEA. Human antibodies to human CEA with improved properties can then be engineered in a number of ways. In Example 1 it is demonstrated how the affinity of the human anti-CEA antibody can be improved by oligonucleotide directed mutagenesis of the complementarity determining regions (CDR's) of the VH and VL domains of the antibodies. The use of antibody chain shuffling is also demonstrated, for instance combining the VH domains of antibodies derived from one library with the VL domains of another library, thus expanding the pool of VL partners tested for each VH domain. Example 1 also demonstrates the use of this procedure, or a combination of oligonucleotide mutagenesis and VL chain shuffling, to generate new antibodies which have an altered specificity on a range of normal tissues compared to the parental antibody. The antibodies also have an improved affinity for human CEA compared with the parental antibody. It is demonstrated that this procedure is capable of changing the specificity of the original antibody in such a way as to improve its potential performance as a specific tumour targeting agent. Cross-reactivity to a human cell line of normal liver cells is greatly reduced with certain combinations of VH and VL.
The use of anti-CEA antibodies in the treatment and diagnosis of cancer has been the subject of a number of patents (e.g. Matsuoka and Kuroki (1989) Patent no. 4871834; Buchegger and Mach (1991) JP Patent no. 5047507; Chester et al 1995, WO 95/15341). The human antibodies disclosed herein should be valuable for similar applications with the advantage that they will enable the use of repeat treatments due to the absence of the human anti-mouse antibody (HAMA) response (Schroff et al (1985) Cancer Res 45: 879-885; DeJager et al (1988) Proc. Am. Assoc. Cancer Res. 29:377). HAMA responses have a range of effects, from neutralisation of the administered antibody leading to a reduced therapeutic dose, through to allergic responses, serum sickness and renal impairment.
It is shown herein that the human antibodies against human CEA can be effective in tumour localisation in a mouse xenograft model of human adenocarcinoma.